The present invention relates to injection molding machines and relates in particular to such machines having the capability of operating a plurality of molds arranged in series.
The prior art shows injection molding machines having the capability of operating a plurality of molds arranged in series. For example, U.S. Pat. No. 3,707,342, issued to A. Lohman on Dec. 26, 1972 shows two molds spaced apart in tandem with a dual nozzle injection unit positioned therebetween to fill the two molds alternately. No provision is made for separate means to stuff the molds.
An additional prior art patent pertinent to the present invention is U.S. Pat. No. 3,898,030, issued Aug. 5, 1975 to T. G. Bishop entitled Injection-Mold Clamping Unit Having Alternately Ejecting Die Assemblies.
In this disclosure latches 80A and 80B are used to couple separable mold halves 56A and 58A whereby single clamping and ejection units are used for both molds.
A further prior art patent is U.S. Pat. No. Re 28,721 reissued to J. J. Farrell on Feb. 24, 1976 entitled Time Saver Plastic Draw-Back Valve Assembly. This patent discloses a primary reciprocating-screw injection unit 12 and an auxiliary injection piston 50 with a valve 52 for diverting molten plastic flow from the primary unit to the secondary unit thereby isolating the primary unit and permitting the secondary unit to "stuff" mold 32.
Other pertinent machine patents include PCT Publication No. WO 86/01146, dated Feb. 26, 1986 and West German Patent No. 3428780, dated Mar. 13, 1986.
In addition, the prior art shows stack and sandwich mold arrangements wherein the mold cavity plates are disposed back to back separated by an integral hot runner. Representative of stack mold arrangements are U.S. Pat. Nos. 3,723,040, 3,973,892 and 4,400,341. Stack or sandwich mold arrangements are well known in the art; however, their draw backs include a less than optimum operating cycle and lack of versatility in components. Moreover, there is a disadvantage to combining a hot runner and the cavity plates, for example: this necessitates replacement of a complete multiple mold assembly rather than to replace one cavity plate at a time.